Hoist and balancing apparatus

ABSTRACT

A pneumatic hoist having a supported cylinder and a piston in the cylinder, and means for introducing compressed air into the chamber to act on the piston to develop a force for lifting or supporting a load. A pneumatic control system is disclosed for controlling the pressure of compressed air admitted into the chamber and is adapted to selectively introduce air having one of three adjustable predetermined pressures chosen to balance either the weight of the load-attachment means, the combined weight of the load-attachment means and the load, or the weight of a load greater than the combination in order to lower, suspend, or raise the load. A safety valve in the system is arranged to trap the air in the cylinder behind the piston in the event of loss of source pressure so that a suspended load cannot accidentally drop. The control system is actuated by a hand control device which has a built-in safety latch mechanism for tamper-proof operation of the hoist apparatus.

united States Patent McKendrick [54] HOIST AND BALANCING APPARATUS LorneJ. McKendrick, 5131 Surfwood Drive, Milford, Mich. 48042 22 Filed:May27, 1970 21 Appl.No.: 40,863

[72] Inventor:

[51] Int. Cl ..B66d H00 [58] Field of Search ..254/l68, 186

[56] References Cited UNITED STATES PATENTS 3,421,737 1/1969 Ulbing..254/186 3,428,298 2/1969 Powell.. ...254/l68 3,260,508 7/1966Powell..... ...254/l68 3,547,155 12/1970 Ulbing ..254/l68 X 3,457,8377/1969 Powell ..254/186 X 3,547,150 12/1970 Geiger ...254/l68 X3,481,583 12/1969 Ulbing ..254/ l 68 FLU/D SOURCE Primary Examiner-EvonCL Blunk Assistant Examiner-Merle F. Maffei Attorney-Hauke, Gifford andPatalidis ABSTRACT A pneumatic hoist having a supported cylinder and apiston in the cylinder, and means for introducing compressed air intothe chamber to act on the piston to develop a force for lifting orsupporting a load. A pneumaticcontrol system is disclosed forcontrolling the pressure of compressed air admitted into the chamber andis adapted to selectively introduce air having one of three adjustablepredetermined pressures chosen to balance either the weight of theload-attachment means, the combined weight of the loadattachment meansand the load, or the weight of a load greater than the combination inorder to lower, suspend, or raise the load. A safety valve in the systemis arranged to trap the air in the cylinder behind the piston in theevent of loss of source pressure so that a suspended load cannotaccidentally drop. The control system is actuated by a hand controldevice which has a built-in safety latch mechanism for tamper-proofoperation of the hoist apparatus.

l 1 Claims, 7 Drawing Figures PATENTEDJuL 1 1 m2 P/LOT PRSSl/RE INVENTORLORNE J- MCKENDRICK BY g ATTORNEYS SHEET 2 OF 3 I-IOIST AND BALANCINGAPPARATUS REFERENCE TO RELATED APPLICATIONS The present application isrelated to my copending applications Ser. No. 733,610 filed May 3l, 1968for- Hoist and Balancing Apparatus," now U.S. Pat. No. 3,537,686 Ser.No. 763,827 filed Sept. 30, 1968, now Pat. No. 3,552,720 for BalancingApparatus for Hoists and Ser. No. 22,986 filled Mar. 26, 1970, for LoadBalancer.

BACKGROUND OF THE INVENTION 1. Field ofthe invention This inventionrelates to pneumatic hoists adapted to raise, lower and counterbalance aload in a suspended position to permit an operator to manually positiona relatively heavy load, and more particularly to a device of thischaracter having a novel control circuit for controlling the pressure ofthe air admitted into the hoist, a safety valve actuated in the event ofloss of air pressure at the source to prevent a. suspended load fromdropping and novel remote control means for actuating the controlcircuit.

ll. Description of the Prior Art A fluid operated hoist comprising asupported cylinder having a fluid pressure responsive piston connectedto a load which is to be raised or lowered is disclosed in the prior artin British Pat. No. 590,413 and U.S. Pat. No. 2,176,979. In order to addto the raising and lowering functions of such hoists, means have beendisclosed in the prior art which adapt the hoist for counterbalancingloads of different predetermined weights. For example, a systememploying a first pressure regulating means between the source of thepressurized fluid and the chamber for reducing the source pressure tobalance the weight of the load-attachment means, and a second pressureregulating means between the source and the cylinder to reduce thesource pressure to balance the combined weight of the attachment meansand the load was disclosed in U.S. Pat No. 2,613,903 H. T. Platz.

One purpose of the present invention is todisclose a novel form ofpneumatic control circuit for such a hoist which adapts the hoist tocounterbalance a plurality of loads of different predetermined weightsand to provide a safety valve in such a control circuit to prevent theaccidental dropping of a suspended load in the case of a loss of sourcepressure.

A further purpose of the present invention is to provide an improvedhand control unit for actuation of the pneumatic system to raise orlower the load incorporating a tamper-proof safety. lock so that theselected raised or lowered position of the load cannot be accidentallychanged without releasing the lock first.

SUMMARY OF THE PRESENT INVENTION The preferred embodiment of the presentinvention comprises a pneumatic hoist having a cylinder adapted forattachment to an overhead support such as a trolley rail or the like, apressure responsive piston disposed in the cylinder to form a fluidpressure chamber and a hoist cable which passes around pulleys containedin the cylinder and which are responsive to movement of the piston totake up or unreel the cable, the other end of which is adapted forattachment to a load.

In one form of the hoist mechanism, one set of pulleys is fixed againstmotion in the center of the cylinder and the other set is carried by aguide piston connected by a pair of piston rods which pass on eitherside of the fixed set of pulleys to the pressure responsive piston. Theadmission of compressed air into the chamber forces the piston towardthe center of the cylinder so that the movable pulleys carried at theopposite end of the piston separate from the fixed set of pulleyscausing the cable to be drawn into the cylinder a distance equal to thepiston stroke, multiplied by the number of pulleys. When the piston ismoved away from the center of the cylinder, the movable set of pulleysapproach the fixed set to allow the cable to lower the load. The presentpneumatic pressure control system however is adaptable for use withother known pneumatic hoists.

The control system essentially comprises a pilot operated main controlvalve disposed in the fluid line between the source of air pressure andthe pressure chamber in the cylinder and a safety valve disposed betweenthe main control valve and the pressure chamber.

Because the hoist employs positive air pressure in each of itspressurized conditions, the preferred system readily adapts itself toasafety feature for preventing the load from being accidentally droppedupon the occurrence of an abnormal drop in the source pressure, as whena line is ruptured. The safety feature comprises a safety valveconnected between the outlet of the main control valve and the inlet ofthe pressure chamber which is controlled by a pilot connection to thesource of the air pressure for sensing an abnormal drop in the airpressure. When such a drop occurs, the safety valve closes before thedrop in pressure can be reflected in the output of the main controlvalve. When the safety valve closes, it traps the air pressure in thepressure chamber behind the piston so that if the hoist is in abalancing condition, the load is locked in a suspended position. Thissafety feature thereby eliminates the possibility of the operator beinginjured by a dropped load and obviates the possibility of a load beingdamaged by,accidental dropping.

A pilot air pressure regulator with a built-in relief valve is disposedin such a manner that a sample of supply pressure is available at itsinlet. Upon adjustment of the pilot pressure regulator, a regulatedpressure signal is provided via its outlet to the pilot air section ofthe pilot air controlled main control valve. A variable orifice controlvalve is disposed in the line between the pilot pressure regulatoroutlet and the pilot control section of the main control valve. Thepurpose of the variable orifice control valve is to delay the rate offlow of the pilot pressure signal to the pilot section of the maincontrol valve. A flexible composition hose assembly, preferably ofreinforced wire-braid construction, is connected to the pilot airoperated section of the main control valve and is subjected to a sampleof the same pressure as is available to the pilot section of the maincontrol valve as received from the pilot pressure regulator unit.

The opposite end of this hose or air line is affixed to a rotaryactuator valve arranged in a convenient hand control unit for operationand control of the hoist by the operator. The hand control unit isconstructed so that it provides for two or more positions allowing airpressure supplied to it to pass to the atmosphere at a controlled rate.The rate at which the air pressure escapes is determined by pre-settingof variable orifices placed in each of the connecting passages disposedbetween the inlet to the hand control unit and the various exhaustoutlets, depending on the position of the valve spool in relation to theinlet supply pilot pressure to the hand control unit. In all instances,the hand control unit has one position which positively restricts anyflow of air from escaping to the atmosphere.

The improved hand control unit has a safety latch mechanism built in soas to be tamper-proof. Thus, a deliberate release of the latch must beeffected in order to change the position of the hand selector controlfrom a low pressure setting to a higher pressure setting. This safetymechanism also guards against shifting the selection from the highpressure position to a lower or near zero pressure setting, unlessdeliberately actuated. The internal safety lock mechanism is controlledby a finger or thumb switch linked to it and actuatable from an externallocation conveniently located on the hand control unit.

The hand control unit therefore, depending on the pre-set adjustment ofthe bleed controls, will directly affect the control signal to the mainpressure control valve by varying the magnitude of the signal to thepilot section of the pilot pressure regulator. In the non-bleed orclosed position of the hand control unit, the pilot signal line pressurewill be at maximum pressure as determined by the setting of the pilotpressure regulator. This pressure signal will cause the main controlvalve to respond proportionately to supply sufficient pressure to thepiston area of the cylinder to lift the total load attached to thelifting cable. Subsequent selections of the hand control unit to connectthe pilot hose to any alternate communication with the atmosphere willreduce the pilot signal to a lesser value. The main control valve willbe responsive to this pressure reduction .and will react to lower itsdelivery pressure so that the load will lower at a rate controlled bythe orifice size in any one of the bleed connections of the hand controlunit as selected.

There are other important advantages inherent in the present improvedpneumatic control system. Because the pilot pressure hose of the handcontrol unit is always vulnerable to being cut or otherwise damaged andsince a lesser pressure in this line or a total loss of the air pilotpressure signal, as would be caused by a completely severed line, wouldcause the load to drop which could cause damage or injury, this hose hasbeen wire reinforced to reduce the liklihood of this occurring.

The internal safety latch incorporated in the hand control unit, whichis of a non-tamper nature, removes the tendency for a hoist controloperator, as a matter of convenience in operation, to file, grind off orin any other way eliminate the safety latch and to thus make theapparatus unsafe for general use.

As heretofore mentioned, an additional safety valve is disposed betweenthe outlet of the main control valve and the inlet to the hoist cylinderchamber. The safety valve is designed so as not to impair the normal airflow rate through it during normal hoist operations. However, in theevent of a sudden air flow rate due to mis-selection of a high controlpressure with no load on the hoist lifting cable, or in the event thatthe load should become accidentally disconnected, the safety valve willrestrict the flow rate, thereby causing a significant reduction in thespeed of retraction of the cable.

Briefly, the improved pneumatic control system essentially provides amonostat in the form of a remote pilot operated main control valvefitted to the balancing hoist cylinder inlet. Upon attaching the airsupply of about 80 psi. to the inlet of a one-way check valve, airpressure is available to the inlet of the monostat or main controlvalve. Upon attaching a load to the free end of the cable, adjustment ofthe pilot pressure regulator to increase the regulated output pressurewill balance the weight by providing sufficient air pressure over thepiston area to support the weight. Upon pulling down on the load, themonostat inlet pressure controlling section will close and a reliefsection will detect the increase in air pressure within the cylinderchamber of the hoist due to compressing ofthe trapped air. Thisincreased pressure will cause the relief section of the monostat toopen, thus bleeding off the excess pressure and thereby maintaining acontinued balancing of the load. This control arrangement, when appliedto a hoist concept such as disclosed for instance in the aforementionedcopending application Ser. No. 733,610 now U.S. Pat. No. 3,537,686,provides a complete balancing effect over the full cable travel of thebalancer unit.

Upon lifting or exerting an upward force on the supported load, thepiston will move toward the center section, causing a drop in cylinderpressure. The monostat senses this pressure drop and opens to provideadditional air pressure to replenish and maintain the pressure in thechamber, and to thus maintain the load in balance.

Thus, it can be seen that the preferred pneumatic control system adds tothe capability and safety of air hoists of the cylinder and piston type.Other advantages of the present invention will readily become apparentto those skilled in the art to which the invention pertains uponreference to the following detailed description.

DESCRIPTION OF THE DRAWINGS The description refers to the accompanyingdrawings in which like reference characters refer to like partsthroughout the several views, and in which:

FIG. 1 is a view showing a preferred air hoist and balancing apparatusand including a schematic representation of an improved pneumaticcontrol system for the hoist and balancing apparatus;

FIG. 2 is a cross-sectional view of the balancer shown in FIG. 1;

FIG. 3 is a schematic view of a preferred pneumatic control systemshowing a master pressure regulator valve in cross section and on anenlarged scale;

FIG. 4 is a cross section through the improved hand control unit for thehoist mechanism shown in FIG. 1; v

FIG. 5 is a transverse cross section through the hand control unit shownin FIG. 4 and as seen along line 5 5 thereof;

FIG. 6 is another transverse cross section through the hand control unitshown in FIG. 4 and as seen along line 6 6 thereof; and

FIG. 7 is a longitudinal cross section through a portion of a preferredpneumatic safety cable for the pilot air pressure line connected betweenthe hand control unit and the main control valve.

DESCRlPTlON OF THE PREFERRED EMBODIMENT Now referring to the drawings,FIGS. 1 and 2 illustrate a representative air hoist and balancingapparatus generally indicated at 10 as comprising an air hoist l2 and apneumatic control system 14 connected with the air hoist 12. The hoistcomprises an elongated cylinder 16 having an end housing 18 closing oneend of the cylinder. A support plate 20 at the other end of the cylinderis connected to the end 18 by rods 22. Sup port members 24, attached tothe cylinder 16, are adapted to support the cylinder on suitableoverhead support means, such as a rail 25 or the like, attached to theceiling of a building to enable the hoist to be moved horizontally. Apressure responsive piston, indicated at 26, is slidably disposed in thecylinder 16 and is preferably connected to another piston 28 by rod 30so that the two pistons move together within the cylinder, as more fullydisclosed in my aforementioned U.S. Pat. No. 3,537,686.

The edges of the piston 26 are sealingly engaged with the walls of thecylinder 16 to form a fluid pressure chamber 32 between the piston 26and the support plate 20.

Motion of the piston 26 away from the support plate 20 is produced bythe introduction of compressed air into the chamber 32. Motion of thepiston 26 toward the support plate 20 reduces the volume of the chamber32.

A load-supporting cable 42 having one end anchored in the cylinder 16and wrapped around a set of fixed and movable pulleys 44 and 45respectively in a manner known in the art has its other end extendingthrough an opening in the cylinder for securement to a hook 46 to form aload-attachment means which is adapted to support a load 48 having apredetermined weight. The cable 42 is arranged so that as the movablepulleys 44 separate from the fixed pulleys 45 by means of movement ofthe piston 26 the hook 46 is raised toward the cylinder 16 and as themovable pulleys 44 move toward the fixed pulleys 45, the hook 46 ismoved down away from the cylinder 16. The relative motion between thetwo sets of pulleys, as more fully described in my aforementioned U.S.Pat. No. 3,537,686, causes the hook 46 on the end of the cable to move adistance which is a function of the stroke of the piston 26 multipliedby the number of pulleys employed.

The load 48, for purpose of illustration, is described as having apredetermined weight, which is typical in a production line where thehoist 10 is employed for positioning a succession of identicalworkpieces in a fixture, each of the workpieces having the same weight.The pneumatic control system 14 is adjusted to accommodate this weightand, as illustrated, provides a connection between a source 50 of fluidunder pressure, such as compressed air, and the fluid chamber 32 of thecylinder 16. The control system allows the operator to introduce airinto the chamber 32 having a selected one of three predeterminedpressures, each of which corresponds to the balancing pressure of apredetermined weight. One of the predetermined pressures when introducedinto the chamber 32 balances the piston 26 and the weight of the hook 46and cable 42. A second higher pressure can be selected to balance thecombined weight of the hook 46, the cable 42 and the load 48. The thirdor highest pressure is adapted to balance a weight which is in excess ofthe combined weight of the hook 46, the cable 42 and the load 48. Athree position hand control 106 is provided for this purpose and will bedescribed in greater detail below.

To achieve the balance control, the control circuit 14 includes aconduit 52 connecting the source 50 and the inlet of the chamber 32through a main control valve 54in the conduit of the type which respondsto a pneumatic signal by providing a pressure reduction of the sourcepressure to a pressure corresponding to the signal. A check valve 53 isdisposed in the conduit 52 intermediate the source 50 and the controlvalve 54.

As can best be seen in FIG. 3, the monostat or main control valve 54comprises an outer housing 56 containing an inner housing 58. The innerhousing 58 is provided with an upper pilot control chamber 60 adapted tobe in fluid communication with a lower pressure regulating chamber 62 bymeans of a fluid channel 64. The lower pressure regulating chamber 62 isadapted to provide a constant controlled regulated fluid pressure bymeans of suitable valve control mechanism within the housing 58, whichwill be presently described, and is provided with an outlet 66 which isin fluid communication with the hoist cylinder pressure chamber 32through a normally open safety shut-off valve 68. The upper controlchamber 60 and lower pressure regulating chamber 62 are divided by atransverse wall portion 70 extending substantially centrally through thehousing 58. Below the dividing wall portion 70 and spaced therefrom is afloat member 72 of substantially smaller diameter than the internaldiameter of the housing 58, and which provides for increases orreductions in the volume of the lower pressure regulating chamber 62.The float member is provided with an upper diaphragm 74 securedcircumferentially to the upper surface of the float member and to thewall 59 of the inner housing 58 so as to provide an extensible pilotpressure chamber 76 between the dividing wall portion 70 and the uppersurface of the float member 72 and the upper diaphragm 74. The oppositelower surface of the float member 72 is also provided with a diaphragm78 spaced from the upper diaphragm 74 and circumferentially attached tothe bottom surface of the float member and to the wall 59 of the innerhousing 58 so as to provide a radial exhaust chamber between thediaphragms 74 and 78. An exhaust vent 81 connects the chamber 80 to theatmosphere.

The pilot pressure chamber 76 is in communication with the atmosphere bymeans of a bleed orifice 82 extending through the wall 59 of the innerhousing 58. A one-way ball check safety valve 84 is also connected withthe chamber 76 and is adapted to bleed off excess fluid pressure fromthe pilot pressure chamber 76, if the fluid flow or pressure shouldexceed the amount which can nonnally be handled through the bleedorifice 82. Initially, the upper control chamber 60, the lower constantpressure regulating chamber 62 and the pilot pressure chamber 76 are allsupplied with fluid under pressure from the fluid pressure source 50through the fluid line 52, the one-way check valve 53 and an inlet port86 leading into the inner housing 58.

Contained within the upper control chamber 60 is a measuring capsule 88which is fluidly connected by a conduit 90 to a pilot fluid pressureline 92, which in turn is in communication with the outlet of a pilotpressure regulator 94, whose inlet is connected to the fluid supplysource 50 by means of an extension 55 of the main pressure line 52.

A variable orifice control valve 96 is disposed in the line 92 betweenthe pilot pressure regulator 94 and the pilot pressure measuring capsule88 for the purpose of delaying the rate of flow of the pilot pressuresignal from the pilot pressure regulator 94 to the pilot section of themain control valve 54.

The upper control chamber 60 and the pilot pressure chamber 76 areconnected through a valve member 98 which is moved to. an open or closedposition by movement of the pilot pressure measuring capsule 88 inresponse to a signal received from the pilot pressure regulator 94. Thelower pressure chamber 62 and the main fluid supply inlet 86 arelikewise adapted for selective fluid communication through a supplyvalve member 100, which is normally biased into closed position by meansof a spring 102. The supply valve member 100 is interconnected with arelief valve member 104 disposed between the lower pressure regulatingchamber 62 and the exhaust chamber to exhaust excess pressure from thepressure regulating chamber 62 upon upward movement of the float member72.

It will be seen from FIG. 3 that on downward movement of the floatmember 72, the valve willbe opened to admit fluid from the fluid supplysource 50 into the lower pressure regulating chamber 62 and that sincethe position of the float member 72 is determined by the signal receivedin the pilot pressure chamber 76 the supply of fluid through the outlet66 as controlled by the valves 100 and 104 will be in response to to thesignal also. This portion of the control system 14 is disclosed andclaimed in copending application Serial No. 22,986 and forms no part ofthe present invention.

With specific reference to FIGS. 4-6, the manual control unit 106 of thepresent invention comprises a first fixed or stationary body portion 108provided with an inlet fitting 110 adapted to be attached to the pilotpressure line 92 by means of a flexible cable or hose 1 12. The inletfitting 110 is in communication with a pilot pressure chamber 114provided by a coaxial bore 116 through the fixed body portion 108. Atthe inner end of the bore 116, a sealed valve member 118 is providedwhich has an axial orifice 120 of predetermined diameter, and which isbiased toward the inner end of the inlet bore 116 and against a secondbody portion 124 by means of a spring 122 disposed within the pilotpressure chamber 114. The body portion 124 is rotatable relative to thebody portion 108 around a pin 126 extending centrally axially throughthe body portion 124 to be centrally secured against rotation by a lockscrew 128 fastened within the body portion 108.

As can best be seen in FIG. 5, the body portion 124 is provided with apair of radially angularly spaced bleed orifices 130 and 132 which areadapted to be selectively brought into alignment with the inlet pressureorifice 120 through the valve member 118 upon respective clockwise orcounter-clockwise rotation of the rotatable body portion 124. The axialbleed orifices 130 and 132 communicate respectively with a radialorifree 134 and 136 which open to the atmosphere. The fluid flow betweenthe axial bleed orifices 130 and 132 and their respective radicalorifices I34 and 136 to the atmosphere can be manually adjusted by meansof needle valves 138 (FIG. 4), provided in the rotatable body portion124, and which can be screwed in or out to thereby vary the rate offluid flow between the axial bleed orifices 130 and 132 and theirrespective radial bleed orifices 134 and 136. After appropriate initialadjustment of the needle valves 138 as may be required by the particularload lifting operation, the needle valves can be locked in place by theprovision of lock nuts 140.

As can best be seen in FIG. 4, appropriate coaxial positioning of thebleed orifices 130 or 132 with the pilot pressure orifice 120 isaccomplished by the provision of a ball detent means 142, comprising anaperture 144 provided in the rotatable body portion 124, and disposedparallel with the central pin 126 and which contains a ball 146 biasedby a spring 148 towards the fixed body portion 108. The spring 148 isretained within the aperture 144 by means of a spring adjusting andretaining screw 150. The ball 146 is adapted to cooperate withcomplementary angularly spaced detent recesses 152 (FIG. 6) provided inthe fixed body portion 108 in such relation as to correspond to thespacing between the bleed orifices 130 and 132. The angle of rotation ofthe rotatable body portion 124 is normally limited within the angularspacing of the bleed orifices 130 and 132 and the detent recesses 152 bymeans of a pin 154, which is resiliently retained within a radial slot156 in the fixed body portion 108. Thus, upon rotation of the rotatablebody portion, either clockwise or counter-clockwise, when the pin 154abuts against either end of the radial slot 156, the ball 146 will snapinto one of the detent recesses 152 to thereby accurately align thepilot pressure orifice 120 with either bleed orifice 130 or 132 to bleedpilot fluid from the pilot line' 92 through the control line 1 12 in anamount as determined by the preadjustment of the respective needlevalves 138.

The resiliently retained pin 154, in addition to the provision oflimiting the rotation of the rotatable body portion 124, provides asafety latch means by which the rotatable body portion of the manualcontrol unit can be securely locked in an angularly rotated positionrelative to the fixed body portion 108, in which neither bleed orifice130 or 132 is aligned with the pilot pressure orifice 120, so that fluidflow through the manual control unit 106 is completely blocked. Thisoccurs under fullload, maximum pressure conditions desired for the hoistoperation, which causes the main control valve 54 to respondproportionately as determined by the setting of the pilot pressureregulator valve 94 to supply a sufficient pressure over the piston areaof the hoist to lift the total load attached to the cable 42.

The safety mechanism positively locks the hand control in this positionso that with a full load being hoisted the control will not beinadvertently shifted to a position which would permit the load to drop.While hand controls with this type of safety feature have beenpreviously provided, unlike the previous hand controls the control unit106 is constructed so that the safety pin 154 cannot be removed withouttaking the unit apart. In previous devices the hand control could beeasily altered to remove the safety mechanism or to make it inoperablewhen the operator felt it interfered with the speed at which he wantedto operate the device. This of course led to accidents.

To provide the safety latch, the pin 1 54 is resiliently slidablyretained within an aperture 158 in the rotatable body portion 124 and isspring loaded from the rear by means of a spring 160. The rear end ofthe pin 154 adjacent the end of the spring 160 is provided with a nibportion 162 which extends upwardly through a longitudinal slot 164 inthe body portion 124 for longitudinal sliding movement therein. The ribportion 162 extends outwardly of the body portion to connect to a thumbgrip 166. The fixed body portion 108, as seen in FIG. 6, is additionallyprovided with a separate pin recess 168 radially aligned with thecurvilinear pin slot 156 but angularlyspaced therefrom. It can thus beseen that, if the thumb grip 166 is manipulated by movement towards therear of the rotatable body portion 124 so that the nib portion 162 ofthe pin 154 is caused to slide within the slot 164 and to thereby movethe pin 154 out of the curvilinear slot 156 against the force of thespring 160, the rotatable body portion 124 can be rotated beyond theangular position normally permitted by the curvilinear slot 156 to causethe lock pin 154 to snap into the separate pin recess 168 under theforce of the spring 160, thereby locking the rotatable body portion 124against inadvertent or accidental retention. In this position neither ofthe bleed orifices 130 or 132 in the rotatable body portion 124 will bealigned with the pilot pressure orifice 120 in the fixed body portion108, thus completely blocking the fluid flow through the hand controlunit 106. Also in this position, the pilot signal line pressure will beat a maximum as determined by the preadjustment of the pilot pressureregulator 94. This maximum pilot pressure signal causes operation of themain control valve 54 to supply maximum fluid pressure into the cylinderchamber 32 of the hoist for lifting and supporting the weight attachedto the cable 42. When the thumb grip 166 is actuated to move the lockpin 154 again back into the curvilinear slot 156, the rotatable bodyportion 124 can be rotated within the limits of the slot 156 to aligneither bleed orifice 130 or 132 with the pilot pressure 120 to obtainany selected intermediate pressure position between near zero pressureand the maximum pressure as determined by the adjustment of the needlevalves 138. The amount of pilot air bled through the orifices and 132causes a signal to be transmitted to the pilot pressure regulator 94,which transfers the signal to the measuring capsule 88 in the uppercontrol chamber 60 of the main control valve 54 to selectively open thevalve 98 between the upper control chamber 60 and the pilot pressurechamber 76 to thereby correspondingly regulate the pressure in thepressure regulating chamber 62.

With additional reference to FIG. 7, the flexible hose or conduit 112connecting the hand control unit 106 to the pilot pressure line 92 ispreferably a steel wire reinforced hose and comprises, as particularlyseen in cross section in FIG. 7, an outer elastomer tube which may be ofneoprene, rayon or the like, which retains an intermediate tube of steelwire braid 172 for reinforcement of the hose, to which is bonded aninner liner 174 of plastic or elastomer fibers or the like. Thisconstruction for the flexible hose 112 is preferred to prevent the hosefrom being severed or punctured.

Referring back to FIG. 3, and as briefly mentioned before, a safetyshut-off valve 68 is disposed between the main control valve 54 and thecylinder chamber 32 of the hoist. The valve 68 is connected to the fluidsupply source 50 by means of a line 176 which normally, that is undernormal air pressure or fluid pressure, retains the valve in an openposition so as not to restrict the fluid flow between the outlet 66 ofthe main control valve 54 and the cylinder chamber 32. However, in theevent that the fluid pressure should drop below a safe value, the valve68 will be forcibly closed by means of a spring a sole noid or othermeans to thereby block further fluid flow between the main control valve54 and the cylinder chamber 32 and trapping fluid at a safe pressurewithin the cylinder chamber 32, thus preventing sudden movement of thepiston 26 which otherwise would cause the load attached to the cable 42to rapidly drop.

Thus, it can be seen that l have described in detail an improvedpneumatic control system for a hoist and balancing unit using positivefluid pressure at all times to raise, lower or balance a load of apredetermined weight. The preferred system has a number of advantagesover other systems utilizing a predetermined bleed control where once apositive pressure has been established to support a load and itsattachment, the lowering and unloading of the load is accomplished bybleeding some of the pressure to the atmosphere.

By providing the control system with three predetermined balancedpressures that can be admitted into the hoist, the following advantagesare available. When the load attachment means alone is in a state ofbalance, the operator with a slight effort can move the hook up and downthrough the complete range of the hoist cable travel without operatingthe hand control unit. After manually lowering the hook to a positionwhere it can be attached to the load, it remains positioned so that itcan be attached to the load. After the load has been attached, the handcontrol unit can be repositioned to the position associated with thehighest pressure so that the air pressure behind the piston issufficient to support as well as raise the load. Normally the differencebetween the pressure associated with raising the load and the pressurefor balancing the load in a suspended position is adjusted or trimmed sothat with the higher pressure, due to the inherent friction in thesystem, the hoist does not raise the load until the operator manuallyassists in raising the load upward. Once the friction forces in thesystem has been momentarily overcome, the air pressure is thensufficient to keep the piston moving and the hoist to continue liftinguntil the operator applies resistance to the load to stop its motion,whereby the inherent friction in the system then holds the load at rest.The hoist will then support the load in this new position until it ismoved upwardly again. The load can be lowered by the operator byapplying a manual downward force on the load which requires some effort,however, by positioning the remote hand control unit to admit the lowestpressure into the hoist chamber, the load can then be lowered withouteffort. The system can also be adjusted so that the intermediatepressure and the lowest pressure are relatively close so that the loaddoes not automatically commence dropping when the control is shiftedfrom the intermediate pressure to the lowest pressure until the operatorapplies a slight manual downward force to overcome the inherent frictionof the system so that it commences its downward motion.

The control system has a fail-safe feature in that if the air pressureat the source drops, the safety valve traps the pressure existing in thehoist chamber at the occurrence of the pressure drop so that the hoistcontinues to respond to the last signal received by the main controlvalve. Although under these circumstances the operator is unable tochange his selection, he can in fact continue to position the loadalthough he is restricted to the one selection in which the main controlvalve is in at the occurrence of the failure.

Another fail-safe" feature of the present invention is the provision ofa reinforced flexible hose for the remote hand control unit to lessen orto eliminate the danger of the hose being cut or otherwise damaged.

A third fail-safe feature of the present invention is the provision ofthe safety lock incorporated within the hand con trol unit to lock theunit in the maximum pressure position to guard against inadvertent oraccidental shifting of the maximum positive pressure setting to a loweror near zero pressure setting unless deliberately actuated.

Although I have described only one embodiment of my invention, it is tobe understood that various changes and revisions can be made thereinwithout departing from the spirit of the invention as expressed in thescope of the appended claims.

I claim:

1. In a balancing hoist having a pneumatic control system, a hoist,means in said hoist for supporting a cable extending from said hoistadapted to be reeled into and out of said hoist to raise or lower a loadattached to the end of said cable, said means comprising an expansiblepressure chamber and a piston in said chamber, said chamber beingadapted to receive fluid under pressure and said piston being adapted tobe moved in one direction upon an increase in pressure in saidexpansible chamber and in the other direction upon a decrease inpressure in said expansible chamber; a source of fluid under pressure; afirst fluid line connecting said source of fluid to said expansiblechamber; a pilot pressure controlled main control valve in said firstfluid line; a second fluid line between said source of fluid pressureand the inlet of a pilot pressure regulator; a third fluid lineconnecting the outlet of said pilot pressure regulator with the pilotsection of said main control valve for supply of pilot pressure thereto;a fourth fluid line comprising a vent line connected to said pilotpressure regulator; a vent control means connected to the other end ofsaid vent line, said vent control means having at least two positionsselectively connectable to said vent line for venting said vent line atrates different from each other, and a third position for blocking saidvent line, each of said positions applying a pilot pressure controlsignal to said pilot pressure regulator of different magnitudes fortransmission to said main control valve to thereby selectively vary thepressure supplied to said expansible chamber by said main control valve;said vent control means including a housing having a first body portionsecured to said vent line, said first body portion having a pilotpressure inlet orifice aligned and in communication with said vent line,a second body portion secured to said first body portion and rotatablerelative thereto, said second body portion having angularly spaced ventmeans selectively adaptable to be aligned with said pilot pressure inletorifice of said first body portion in a first and a second position,said second body portion being rotatable to a third position in whichneither of said vent means of said second body portion will be alignedwith said pilot pressure inlet orifice of said first body portion, saidsecond body portion being provided with means to normally limit rotationof said second body portion relative to said first body portion betweensaid first and second positions and to lock said second body portion insaid third position, the improvement comprising said last mentionedmeans comprising a pin carried within said second body portion; acurvilinear slot provided in said first body portion, biasing meanscarried by said second body portion for urging said pin into engagementwith said curvilinear slot when said second body portion is in eithersaid first or second position, said curvilinear slot being entirelyenclosed by said body portions whereby said pin is entirely enclosed bysaid body portions, said curvilinear slot having an angular dimensioncorresponding to the angular spacing between said vent means, said pinbeing provided with means for moving said pin out of said curvilinearslot for rotation of said second body portion to said third position inwhich neither of said vent means is aligned with said pilot pressureinlet orifice in said first body portion to thereby block fluid flowthrough said vent control means; and a recess within said first bodyportion and arcuately spaced from said curvilinear slot, said recessreceiving saidpin when said second body portion is moved to said thirdposition to lock said second body portion in said third position, saidbiasing means urging said pin into said recess when said second body isin said third position.

2. The pneumatic control system as defined in claim 1 further comprisingflow control means disposed in said third fluid line between said pilotpressure regulator and said main control valve to delay the transmissionof pilot pressure signal from said pilot pressure regulator to the pilotsection of said main control valve.

3. The pneumatic control system as defined in claim 1 the I furtherprovision of a one-way check valve disposed between said source of fluidunder pressure and said main control valve to prevent back flow of fluidfrom said main control valve to said source of fluid pressure.

4. The pneumatic control system as defined in claim 1, a check valveprovided in said first fluid line adapted toclose the supply of fluid tosaid main control valve upon an increase in fluid flow beyond thepredetermined normal operating flow.

5. The pneumatic control system as defined in claim 1, the furtherprovision of a safety shut-off valve disposed between said main controlvalve and said expansible chamber, said safety shut-off valve having avalve operating member connected to said source of fluid under pressureto thereby maintain said valve in an open position for freecommunication of fluid between said main control valve and saidexpansible chamber, and means to close said safety shut-off valve upon adecrease in fluid pressure at said source of fluid under pres- I surebelow a predetermined value.

6. The control system as defined in claim 1, said vent means of saidsecond body portion comprising bleed orifices to bleed pilot pressure tothe atmosphere to thereby produce a signal transmitted to the pilotpressure regulator to cause said main control valve to change thepressure supplied to said expansible pressure chamber.

7. The control system as defined in claim 6, the flow through said bleedorifices being manually adjustable to obtain a first pressure setting oflow magnitude and a second pressure setting of a higher magnitude.

8. The control system as defined in claim 1, the second body portionbeing provided with resilient detent means adapted to cooperate withangularly spaced recesses provided in said first body portion spaced adistance equal to the distance between said bleed orifices to accuratelyselectively align either of said bleed orifices with the pilot pressureinlet orifice of said first body portion.

9. The control system as defined in claim 1, said first body portionbeing provided with a recess angularly spaced from said curvilinear slotadapted to receive said pin when said second body portion is rotated tosaid third position to thereby positively lock said second body portionagainst rotation.

10. The control system as defined in claim 9, said pin being resilientlyforced into engagement within said locking recess of said first bodyportion and provided with a grip means extending outwardly of saidsecond body portion to move said pin out of said locking recess.

11. The control system as defined in claim 1, said vent line comprisinga flexible reinforced wire braided hose.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No-3,675,899 Dated July 11. I972 Inventor(s) Lorne J. McKendriok It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

IN THE SPECIFICATION Col. 1, line 38, after "2,613,903" insert to C INTHE CLAIMS Claim 8, line 1, should be 6- Claim 10, "9" should be l-Signed and sealed this 27th day of February 1973.

(SEAL) Attest:

EDWARD M. FLETCHERJR. ROBERT GOTTSCHALK Attesting Officer Commissionerof Patents FORM FO-105 O (IO-69) USCOMM-DC 60376-P69 U.S. GOVERNMENTPRINTING OFFICE: I959 O366-336

1. In a balancing hoist having a pneumatic control system, a hoist,means in said hoist for supporting a cable extending from said hoistadapted to be reeled into and out of said hoist to raise or lower a loadattached to the end of said cable, said means comprising an expansiblepressure chamber and a piston in said chamber, said chamber beingadapted to receive fluid under pressure and said piston being adapted tobe moved in one direction upon an increase in pressure in saidexpansible chamber and in the other direction upon a decrease inpressure in said expansible chamber; a source of fluid under pressure; afirst fluid line connecting said source of fluid to said expansiblechamber; a pilot pressure controlled main control valve in said firstfluid line; a second fluid line between said source of fluid pressureand the inlet of a pilot pressure regulator; a third fluid lineconnecting the outlet of said pilot pressure regulator with the pilotsection of said main control valve for supply of pilot pressure thereto;a fourth fluid line comprising a vent line connected to said pilotpressure regulator; a vent control means connected to the other end ofsaid vent line, said vent control means having at least two positionsselectively connectable to said vent line for venting said vent line atrates different from each other, and a third position for blocking saidvent line, each of said positions applying a pilot pressure controlsignal to said pilot pressure regulator of different magnitudes fortransmission to said main control valve to thereby selectively vary thepressure supplied to said expansible chamber by said main control valve;said vent control means including a housing having a first body portionsecured to said vent line, said first body portion having a pilotpressure inlet orifice aligned and in communication with said vent line,a second body portion secured to said first body portion and rotatablerelative thereto, said second body portion having angularly spaced ventmeans selectively adaptable to be aligned with said pilot pressure inletorifice of said first body portion in a first and a second position,said second body portion being rotatable to a third position in whichneither of said vent means of said second body portion will be alignedwith said pilot pressure inlet orifice of said first body portion, saidsecond body portion being provided with means to normally limit rotationof said second body portion relative to said first body portion betweensaid first and second positions and to lock said second body portion insaid third position, the improvement comprising said last mentionedmeans comprising a pin carried within said second body portion; acurvilinear slot provided in said first body portion, biasing meanscarried by said second body portion for urging said pin into engagementwith said curvilinear slot when said second body portion is in eithersaid firSt or second position, said curvilinear slot being entirelyenclosed by said body portions whereby said pin is entirely enclosed bysaid body portions, said curvilinear slot having an angular dimensioncorresponding to the angular spacing between said vent means, said pinbeing provided with means for moving said pin out of said curvilinearslot for rotation of said second body portion to said third position inwhich neither of said vent means is aligned with said pilot pressureinlet orifice in said first body portion to thereby block fluid flowthrough said vent control means; and a recess within said first bodyportion and arcuately spaced from said curvilinear slot, said recessreceiving said pin when said second body portion is moved to said thirdposition to lock said second body portion in said third position, saidbiasing means urging said pin into said recess when said second body isin said third position.
 2. The pneumatic control system as defined inclaim 1 further comprising flow control means disposed in said thirdfluid line between said pilot pressure regulator and said main controlvalve to delay the transmission of pilot pressure signal from said pilotpressure regulator to the pilot section of said main control valve. 3.The pneumatic control system as defined in claim 1 the further provisionof a one-way check valve disposed between said source of fluid underpressure and said main control valve to prevent back flow of fluid fromsaid main control valve to said source of fluid pressure.
 4. Thepneumatic control system as defined in claim 1, a check valve providedin said first fluid line adapted to close the supply of fluid to saidmain control valve upon an increase in fluid flow beyond thepredetermined normal operating flow.
 5. The pneumatic control system asdefined in claim 1, the further provision of a safety shut-off valvedisposed between said main control valve and said expansible chamber,said safety shut-off valve having a valve operating member connected tosaid source of fluid under pressure to thereby maintain said valve in anopen position for free communication of fluid between said main controlvalve and said expansible chamber, and means to close said safetyshut-off valve upon a decrease in fluid pressure at said source of fluidunder pressure below a predetermined value.
 6. The control system asdefined in claim 1, said vent means of said second body portioncomprising bleed orifices to bleed pilot pressure to the atmosphere tothereby produce a signal transmitted to the pilot pressure regulator tocause said main control valve to change the pressure supplied to saidexpansible pressure chamber.
 7. The control system as defined in claim6, the flow through said bleed orifices being manually adjustable toobtain a first pressure setting of low magnitude and a second pressuresetting of a higher magnitude.
 8. The control system as defined in claim1, the second body portion being provided with resilient detent meansadapted to cooperate with angularly spaced recesses provided in saidfirst body portion spaced a distance equal to the distance between saidbleed orifices to accurately selectively align either of said bleedorifices with the pilot pressure inlet orifice of said first bodyportion.
 9. The control system as defined in claim 9, said pin beingresiliently forced into engagement within said locking recess of saidfirst body portion and provided with a grip means extending outwardly ofsaid second body portion to move said pin out of said locking recess.10. The control system as defined in claim 1, said vent line comprisinga flexible reinforced wire braided hose.